1. Field of the Invention
The present invention relates to a weight sensor device used in a seat, for measuring a weight of an occupant seated on the seat in an automobile or the like.
2. Description of the Related Art
A mat type or electrostatic-capacitance type weight sensor device is known which is used to measure a weight of an occupant seated on a seat of an automobile or the like.
The conventional mat type weight sensor device includes a plurality of pressure sensors arranged on a plastic film. Each of the pressure sensors output a signal indicative of electrical resistance corresponding to the applied pressure thereto. The pressure sensors are interposed between a cushion pad made of urethane foam or the like and a facing sheet thereof. In this configuration, the outputs from the pressure sensors are processed by an operation unit mounted in an automobile or the like, to determine a weight of an occupant seated on the seat.
The conventional electrostatic-capacitance type weight sensor device, on the other hand, has two electrodes facing each other. The electrodes are attached to a cushion spring disposed on a seat cushion frame for improving a feeling to ride in. In this configuration, electrostatic capacitance between the electrodes, which changes according to contraction and expansion of the cushion spring, is measured to thereby determine a weight of an occupant seated on the seat.